The present invention relates to water heaters and more particularly to a foam insulated water heater construction, a method of manufacturing a foam insulated water heater, and a collar device for use in a foam insulated water heater construction to prevent foaming insulating material from covering heater controls.
Typically, water heaters are formed of an inner water tank with an outer shell located over the inner tank with a space therebetween. The space between the inner tank and outer shell is filled with a thermal insulation. For many years fiber glass has been used as the insulation material between the inner tank and outer shell. More recently, a foam such as urethane, has been used as the thermal insulation material in place of fiber glass between the inner tank and outer shell. Typically, the foamable material is injected into the space between the inner tank and outer shell, and is allowed to foam in situ.
A problem exists, however, in restraining the foam in desired locations within the space. For example, electric and gas water heaters have heating control apparatus located at and attached to the exterior surface of the inner water tank. It is, of course, important that these controls not be covered with insulating foam.
Various methods and devices have been used in an attempt to prevent the foam urethane from covering the heating control apparatus. For example, one method of attempting to prevent the urethane foam from covering the control device is to pack the area round the control device with fiber glass to function as a barrier to the urethane foam during the foaming process. A drawback with this method is that the foaming urethane material exerts a sufficiently great force on the fiber glass pack as to dislodge it.
One known attempt to prevent the dislodgement of the fiber glass pack is to fabricate the fiber glass pack much thicker than the width of the space between the inner tank and outer shell so that the fiber glass pack will be highly compressed between the inner tank and outer shell when the shell is located concentrically over the tank to resist the forces generated by the expanding foam insulating material. However, this scheme makes the assembly of the outer shell over the inner tank difficult and slow, and results in inconsistent quality of the finished water heater. It is very difficult to hold the uncompressed fiber glass pack in place on the inner tank while the outer shell is installed over the inner tank because either the thickness of the uncompressed fiber glass pack must, somehow, be compressed to conform to the width of the space between the tank and shell before the shell is placed over the tank, or the shell must be initially located off-center over the tank providing a wide space in the vicinity of the uncompressed pack and then moved to a concentric relationship. This procedure increases the chances of displacing the fiber glass pack during assembly of the shell over the tank and the chances of producing a water heater with the shell off-center relative to the tank.
Even in the event that the fiber glass pack is not dislodged to the extent that the foam by-passes it covering the control device, the fiber glass does not have as great a heat insulating valve as the rigid urethane foam. Therefore, there is a greater heat loss in the area of fiber glass than through the surrounding layer of foam.
U.S. Pat. No. 4,372,028 issued on Feb. 8, 1983 discloses another means for preventing insulating foam from covering the control device of an electric device of an electric water heater. In this patent, an elongated flexible bag having an open top and sealed side and bottom edges has an opening through its side walls. The elongated bag is positioned vertically on the inner tank with the opening through the bag side walls positioned over the control device, and is affixed to the wall of the tank. The outer shell is positioned over the inner tank and the elongated bag is injected with expandable foam. After the foam has been allowed to expand in the elongated bag, the rest of the space between the inner tank and outer shell is filled with expandable foam.
U.S. Pat. No. 4,447,377 issued on May 8, 1977 discloses two other ways for preventing insulating foam from covering the control device of an electric water heater. In one embodiment, an elongated preformed member of fiber glass or premolded polyurethane foam is used to insulate around the control devices. The preformed member is as long as the inner tank is tall and has cut-out openings therethrough for receiving the control devices. The elongated preformed member is placed vertically on the exterior wall surface of the inner tank with the control device projecting through the cut out-openings. Next, a plastic envelope is installed to encompass the outer periphery of the inner tank except for that area covered by the elongated preformed member. The outer shell is then installed over the inner tank, and the envelope is injected with an expandable foam. The envelope is necessary to prevent the expanding foam material from forcing its way into the interfaces between the preformed member and the inner tank and outer shell. It should be noted that it is the plastic envelope and not the elongated preformed member which prevents the foam from covering the control device. In another embodiment, a plastic envelope is installed to completely encompass the outer periphery of the inner water tank. The envelope is provided with welded cut-outs which overlay the control devices. The outer shell is then installed over the inner tank, and the envelope is injected with an expandable foam.
U.S. Pat. No. 4,477,399 issued on Oct. 16, 1984 shows yet another way preventing insulating foam from covering the control device of an electric water heater. An inflatable toroidal tube is inserted in the space between the inner tank and outer shell surrounding the control device, and it is inflated with air. Next, the space between the inner tank and outer shell is injected with expandable foam material. After the foam material has expanded, the tube is deflated and removed.